378 ANNUAL, REPORT SMITHSONIAN INSTITUTION, 1918. 



Potonie from the Harz are now known to be Upper Carboniferous 

 and Devonian, respectively. Nevertheless, the advanced character 

 of the Devonian floras makes it a certain assumption that a some- 

 what similar flora existed during Silurian times. Floras are most 

 fully preserved in continental deposits and these are the first to be 

 destroyed during subsequent cycles of erosion, unless they happen 

 to be deeply buried, and then they may never come to light in sub- 

 sequent times. It is only from Devonian and later times that any 

 considerable number of continental deposits have escaped this fate 

 and are available for our enlightenment. Consequently, terrestrial 

 floras appear upon the scene with apparent suddenness during the 

 Devonian. 



DEVONIAN FLORAS. 



Such Devonian floras as are known — and their distribution in- 

 cludes Spitsbergen ; Bear Island; the maritime Provinces of Can- 

 ada; Maine, New York, Kentucky, and elsewhere in the United 

 States; Russia, Norway, Scotland, Ireland, Bohemia, and Germany 

 in Europe; and Australia in the Southern Hemisphere, as well as 

 scattered localities of minor importance elsewhere — apparently indi- 

 cate a cosmopolitan flora that was very like that of the succeeding 

 Lower Carboniferous times. Many supposed fucoids have been de- 

 scribed from Devonian rocks, but these are for the most part of 

 a very indefinite nature. The gigantic stems of Nematophycus 

 found in both the Silurian and Devonian are recorded from Canada, 

 New York, Ohio, England, Wales, and Germany. Their structure is 

 often preserved and they are indubitable algae, probably representing 

 ancient and giant relatives of the modern Laminarians, which often 

 grow to great size. A type exceedingly abundant and characteristic 

 of the Middle Devonian of the Appalachian region was Spirophyton, 

 which has often been considered as of mechanical origin, but which 

 shows a carbonaceous spirally ascending thallus that passes through 

 the bedding planes of the rock and probably represents an ancient 

 seaweed comparable to a modern Thalassophyllum. Objects ap- 

 parently representing the oogonia of Devonian charaphvtes have been 

 recorded from Ohio and elsewhere. 



The ferns are represented in the Devonian by Asterochlaena, a 

 genus of the family Zygopteridae, which ranged from the Devonian 

 to the Permian ; and by a considerable number of rather widespread 

 genera of not very certain botanical position, such as Sphenopteris, 

 Sphenopteridium, Rhizomopteris, Otidophyton, Dimeripteris, Spi- 

 ropteris, Rhodea, Hostimella, Aneimites, Rhachiopteris, etc. Cer- 

 tain similar but later forms have been shown to be pteridosperms, so 

 that the status of many of these Devonian forms is rendered un- 

 certain. A striking fern-like plant, conspicuous in the Devonian of 



